The Paripueira evaporitic interval of Maceio Sub-Basin - Sergipe/Alagoas basin

THE PARIPUEIRA EVAPORITIC INTERVAL OF MACEIO SUB-BASIN - SERGIPE/ALAGOAS BASIN^*

CLÁUDIO P. FLORENCIO ¹, JUAN J. PUEYO ² and

EVARISTO RIBEIRO FILHO ¹

1Instituto de Geociências, USP, São Paulo, SP.

²Facultad de Geología, Universidad de Barcelona, Spain.

Presented by ANTONIO C. ROCHA-CAMPOS

Lower Cretaceous basins of the eastern Brazilian border are characterised by widespread evaporitic occurrences. In the Sergipe/Alagoas Basin, the Paripueira evaporites indicate the first, restricted marine incursions. Evaporites occur in the Cururipe, Maceió and Paripueira areas in the Alagoas region, corresponding to regional structural depressions. In the Maceió evaporitic Sub-Basin, Paripueira sediments are found at depths below 800m. The whole interval is characterised by thick halite deposits, including shale and carbonate interfingerings, and sandstone towards the base of the section. Strong facies changes between siliciclastic sediments and evaporites indicate successive drawdowns of the brine level. Differences in layer thickness in close well profiles (about 100m) suggest strong tectonic control. The absence of well-defined cycles does not permit internal correlation of saline deposits. Periods of low brine concentration are commonly rich in terrigenous or thin calcareous sediments. Halite predominates in the whole interval. It presents light and dark bands that display 4mm sized crystals. Light bands show absence of primary structures with fluid inclusions. Levels of cubic halite crystals, more than 5mm in size, common in a clay matrix, display displacive growth, probably related to sabkha processes. Under the microscope, halite crystals are subhedral, displaying partially dissolved borders and calcite, dolomite and quartz as solid inclusions. Halite also exhibits variable bromine contents (27 - 104ppm). High anoxic conditions lead to preservation of the organic matter, as shown by high TOC, higher than 13% in marls and shales. (December 10, 1999)

^*

Supported by FAPESP, Proc. 96/03157-0.

Publication Dates

• Publication in this collection
  05 Jan 2001
• Date of issue
  Dec 2000